Accumulated particle size distributions through assemblies, integrations, and tests

Past literature and experiments characterized particle contamination on critical aerospace surfaces (IEST-STD-CC1246 cleanliness Level, particle size distribution). These efforts have commonly focused on the condition of freshly precision cleaned surfaces or particle settling behavior on surfaces exposed to fallout in integration high-bay (nominally ISO 14644-1 Class 8) environments. Resulting Particle Size Distributions (PSDs) influence how optical performance metrics (Percent Area Coverage (PAC), scatter, stray light, Bi-directional Reflectance Distribution Function (BRDF)) are characterized by analysis for real-product applications. At the beginning of life in space applications, optical performance metrics are not verifiable in use. This presentation discusses additional factors that affect how particles accumulate on hardware during a series of realistic exposure, inspection and cleaning phases (precision clean, assembly, integration and test, and transition to use (storage, transport, vibroacoustic events)). Relevant considerations include cleanliness maintenance of components and assemblies (cleaning and inspection access, cross-contamination, particle removal technique, restrictions on personnel/gowning), how Visibly Clean, Highly Sensitive (VC-HS) and/or VC-HS+UV (Ultraviolet light) inspections may affect PSDs, and how cross-contamination to and from surrounding surfaces between payload fairing encapsulation and operation onset can affect PSDs. A framework for a more complex model for particles accumulated over a series of exposure environments, inspections, and cleanings is offered. Ideally the surface particle contamination terms can be correlated with data that contamination engineers can measure or characterize. The approach is intended to guide performance analyses for optical and performance engineers, and to organize contamination stakeholder discussions regarding critical surface protections throughout life.